Digital image processing method and apparatus for brightness adjustment of digital images

Abstract

A method of calculating a brightness balance value for a digital image including a plurality of pixels, comprising the steps of: calculating a spatial activity measure in a plurality of local neighborhoods of pixels of the digital image, each local neighborhood including a plurality of pixels; generating a weighting factor for each of the local neighborhoods of pixels as a function of the spatial activity of the local neighborhoods of pixels, the weighting factors having more than two possible values; and applying the weighting factors to the pixels of the digital image to produce the brightness balance value.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This is a continuation-in-part of application Ser. No. 09 / 568,657, filed May 10, 2000 by Gindele, entitled “Digital Image Processing Method and Apparatus for Brightness Adjustment of Digital Images.”FIELD OF THE INVENTION[0002]The invention relates generally to the field of image processing and more particularly to image processing systems which adjust the brightness characteristics of a digital image.BACKGROUND OF THE INVENTION[0003]Many digital imaging systems include three main components: a mechanism for generating the source digital imagery, a mechanism for processing the digital image data, and a mechanism for visualizing the imagery. As such, many digital imaging systems employ more than one image processing method, or algorithm, designed to enhance the visual quality of the final rendered output. In particular, image processing methods of interest are methods for adjusting the overall balance, or brightness of digital images.[0004...

AI Technical Summary

Benefits of technology

[0022]The present invention has the advantage that the brightness balance of a digital image or a print made from an optical printer can be achieved robustly.

Problems solved by technology

While the method disclosed by Kraft et al. is useful for adjusting the overall brightness and color balance of an optical print, the technology cannot be used directly for adjusting the brightness tone of a digital image.

Thus no digital image is formed by the method disclosed Furthermore, no method for adjusting the brightness tone of digital image is mentioned.

However, the method described by Terashita does not teach a method for adjusting the brightness of a digital image Furthermore, the formulation of the pixel classification on the basis of color and / or chrominance signals rather than luminance signals makes the method more susceptible to noise.

The method taught in U.S. Pat. No. 5,724,456 does not adjust the overall digital image brightness.

The methods described by Hughes et al., Kraft et al, and Terashita all relate to optical printer exposure control and do not teach a method of setting camera exposure or adjusting the brightness of a digital image.

The methods taught by Kraft et al, and Terashita create binary masks which can produce statistically unstable results by virtue of the on / off nature of the inclusion / exclusion logic.

Furthermore, the spatial activity measure used by Terashita is not isotropic (sensed equally in all directions) and therefor less robust than the isotropic measures of spatial activity described by Dondes et al.

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